A critical portion of such body electrodes is the element which actually contacts or engages the body tissue to make electrical signal-transfer contact therewith. Some body tissue leads used for pacemaking purposes rely on an electrode having an enlarged tissue-contacting tip having a blunt or spherical configuration, devoid of any projections or other sharp edges which might cause damage to body tissue. Such electrodes must be firmly positioned against the appropriate location on a body organ, e.g., the heart, and must in some manner be maintained in the desired position, since there is no mechanical engagement of the blunt electrode end with the body tissue. As a consequence, there is a risk that such body-implantable leads of the prior art can become dislocated so as to move out of signal-transfer contact with the desired area of body tissue, such as by active movement of the body or the like.
Another type of prior-art electrical lead includes relatively pointed electrode members which can project into the surface of the desired body tissue, thereby providing a degree of physical engagement between the electrode and the body tissue. It has been found that such pointed electrodes may cause unwanted and unnecessary tissue damage, however, especially when it becomes necessary for a surgeon to reposition the electrode within the body, since such electrodes as used in cardiac pacemaker applications are frequently inserted through a patient's vein with a catheter. Venous repositioning of prior-art electrodes having tissue-engaging pointed members may be sufficiently damaging that it becomes necessary to surgically remove or reposition the electrode by opening up the chest cavity of the patient. The time, trauma, and expense of such a procedure is self-evident.
Accordingly, it is an object of the present invention to provide an improved electrode apparatus for tissue stimulation.
It is another object of the present invention to provide stimulation electrode apparatus having tissue-engaging members which can be repositioned with relatively little or no tissue damage.
It is yet another object of the present invention to provide body implantable electrode apparatus having tissue-engaging members that are selectably retractable into or extendable from the electrode assembly.
It is a further object of the present invention to provide stimulation electrode apparatus having tissue-engaging members which grasp or pinch body tissue to thereby establish a firm hold on said body tissue so as to draw said body tissue into positive signal transfer contact with the electrode tip when said tissue-engaging members are retracted.
Another object of the present invention is to provide stimulation electrode apparatus having a member for facilitating the retraction of the tissue-engaging members.
Another object of the present invention is to provide an improved method for establishing electrical signal communication between body tissue and an electrode.